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<A href="introduction6.htm">Debugging Tools for Windows (WinDbg, KD, CDB, NTSD)</A> &gt; <A href="debugger_reference.htm">Debugger Reference</A> &gt; <A href="debugger_commands.htm">Debugger Commands</A> &gt; <A href="syntax_rules.htm">Syntax Rules</A> &gt; </div>
	<div id="winchm_template_title">Register Syntax</div>
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	<div id="winchm_template_content"><div id="mainSection"><p>The debugger can control registers and floating-point registers.</p>
<p>When you use a register in an expression, you should add an at sign ( <b>@</b> ) before the register. This at sign tells the debugger that the following text is the name of a register.</p>
<p>If you are using MASM expression syntax, you can omit the at sign for certain very common registers. On x86-based systems, you can omit the at sign for the <b>eax</b>, <b>ebx</b>, <b>ecx</b>, <b>edx</b>, <b>esi</b>, <b>edi</b>, <b>ebp</b>, <b>eip</b>, and <b>efl</b> registers. However, if you specify a less common register without an at sign, the debugger first tries to interpret the text as a hexadecimal number. If the text contains non-hexadecimal characters, the debugger next interprets the text as a symbol. Finally, if the debugger does not find a symbol match, the debugger interprets the text as a register.</p>
<p>If you are using C++ expression syntax, the at sign is <u>always</u> required.</p>
<p>The <a href="#Bookmark2025"><b>r (Registers)</b></a> command is an exception to this rule. The debugger always interprets its first argument as a register. (An at sign is not required or permitted.) If there is a second argument for the <b>r</b> command, it is interpreted according to the default expression syntax. If the default expression syntax is C++, you must use the following command to copy the <b>ebx</b> register to the <b>eax</b> register.</p>
<div class="code"><span codelanguage=""><table>
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<th></th>
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<td>
<pre>0:000&gt; r eax = @ebx</pre>
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</table></span></div>
<p>For more information about the registers and instructions that are specific to each processor, see <a href="#Bookmark182">Processor Architecture</a>.</p>
<h3><a id="flags_on_an_x86_based_processor"></a><a id="FLAGS_ON_AN_X86_BASED_PROCESSOR"></a>Flags on an x86-based Processor</h3>
<p>x86-based processors also use several 1-bit registers known as <i>flags</i>. For more information about these flags and the syntax that you can use to view or change them, see <a href="#Bookmark184">x86 Flags</a>.</p>
<h3><a id="registers_and_threads"></a><a id="REGISTERS_AND_THREADS"></a>Registers and Threads</h3>
<p>Each thread has its own register values. These values are stored in the CPU registers when the thread is executing and in memory when another thread is executing.</p>
<p>In user mode, any reference to a register is interpreted as the register that is associated with the current thread. For more information about the current thread, see <a href="#Bookmark1376">Controlling Processes and Threads</a>.</p>
<p>In kernel mode, any reference to a register is interpreted as the register that is associated with the current register context. You can set the register context to match a specific thread, context record, or trap frame. You can display only the most important registers for the specified register context, and you cannot change their values.</p></div></div>	
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